Problem: Annika biked $37 \text{ km}$ this morning and another $x \text{ km}$ in the evening. How many kilometers did Annika bike today? Write your answer as an expression.
Answer: Let's see what happens as the distance biked in the evening increases: Distance biked this evening $\text{(km)}$ Total distance biked today $\text{(km)}$ ${10}$ $37+{10} = 47$ ${20}$ $37+{20} = 57$ ${30}$ $37+{30} = 67$ Distance biked this evening $\text{(km)}$ Total distance biked today $\text{(km)}$ ${x}$ $37+{x}$ The answer: $37+x$